1. Field of the Invention
The present invention relates to one way clutches for use in starters or speed change gears for automobiles, or the like.
2. Description of the Prior Art
FIGS. 8 (a) and 8 (b) are a plan view and a sectional view of a conventional one way clutch, respectively. This one way clutch comprises: a plurality of sprags 51, 51, . . . ; an inner retainer 52, made of a metal, for retaining inner portions 51a of sprags 51; an outer retainer 53, made of a metal, for retaining outer portions 51b of the sprags 51; and an annular ribbon spring 55 for urging the sprags 51 in the clockwise direction in FIG. 8 (a). The outer retainer 53 and the inner retainer 52 have flange portions 53b and 52b, respectively, at one axial end thereof. The one-way clutch is to be interposed between inner and outer rings, which are not shown.
In the above-described one way clutch, when the inner ring rotates clockwise in FIG. 8 (a), the sprags 51 respectively tilt toward an idling side (counterclockwise) about inner portions 51a of the sprags 51 owing to frictional contact between the inner portions 51a of the sprags 51 and the inner ring As a result, the rotating torque of the inner ring will not be transmitted to the outer ring, causing the inner ring to idly rotate.
On the other hand, when the inner ring rotates counterclockwise in FIG. 8 (a), the sprags 51 respectively rotate clockwise about the inner portions 51a thereof owing to frictional contact between the inner portions 51a of the sprags 51 and the inner ring. As a result, the inner and outer rings are locked by the wedging action of the sprags 51, allowing the rotating torque of the inner ring to be transmitted to the outer ring.
However, the conventional one-way clutch has problems of being heavy and expensive since its inner and outer retainers 52 and 53 are both made of a metal.
Recently, in order to provide a lighter one-way clutch at a lower cost, it has been proposed to make the outer retainer plastic, less strength being required for the outer retainer than the inner retainer that retains swinging center portions of the sprags (see Japanese Patent Laid-Open Publication No. 63-303232).
However, the one-way clutch, even with the improvement that the outer retainer is made of a plastic, could not attain sufficient reduction in weight and cost, due to the fact that its inner retainer is still made of a metal.